The present invention relates to turbine rotors suitable for use in turbocharges, gas turbines, and the like.
Recently, turbine wheels of turbine rotors have been made of ceramics in ordet to reduce the overall weight of the turbine rotor, as well as to improve the acceleration response of the turbine and to increase the resistance to high temperature gases. Since a turbine wheel rotates at a high speed in a high temperature environment, to attain a high reliability, high strength at elevated temperature and high fracture toughness, the material of the turbine wheel is generally sintered silicon nitride ceramics having substantially no pores.
However, ceramics have a lower fracture toughness than metals, and hence there is a tendency for a ceramic turbine wheel to break due to oxide scale material entering the turbine rotor from the exhaust manifold.
It is an object of the present invention to eliminate this problem.